Method of determining center of gravity and body weight

ABSTRACT

Disclosed is a system, apparatus and method for gathering physiological data. Basic to the system of the present invention is a rigid body mold having preferably a negative impression of the dorsal half of the body. By connecting and/or embedding sensors to the body mold at specific locations, e.g., accelerometers, thermistors, and electrocardiogram electrodes, the sensors will be accurately and reproducibly positioned next to a specific body location each time the subject lies in the body mold. The body mold can be used to insulate the body from external motions thereby facilitating the preparation of a ballistocardiogram. The exact re-positioning of the body in the mold allows exact determination of the center of gravity in the horizontal plane of the body.

This is a division of application Ser. No. 786,746, filed on Oct. 11,1985 now U.S. Pat. No. 4,681,098.

FIELD OF THE INVENTION

The present invention relates to the field of medical instrumentationand methods of using such instrumentation in an accurate andreproducible manner. In particular the present invention concerns use ofgravity and a body mold of a subject to facilitate use of sensors togather physiological data.

PRIOR ART

To measure physiological conditions, electronic or other types ofsensors are often used to gather desired physiological data. Forexample, to estimate temperature, a thermistor can be used. And toestimate the volume of blood passing through the heart in a given periodof time, an accelerometer can be used. Other examples of sensors arecommonly known and include without limitation an electrocardiogramelectrode and a stethoscope metal bell end piece. For other examples seeU.S. Pat. Nos. 3,910,257 and 4,129,125. See also Ballistocardiographyand Cardiovascular Therapy, Proceedings of the Second World Congress onBallistocardiography Cardiovascular Dynamics, Oporto 1969, pages 343-353(New York, 1970).

To use some of the electronic sensors mentioned above, the sensor istypically strapped, suction-cupped or otherwise affixed directly to thehuman body at desired specific body locations. See for example U.S. Pat.No. 3,910,257. It is obviously important to firmly position theelectrodes and sensors in an exact location on the patient to reduce thechances of error and to attempt to achieve reproducible results.However, due to the typical methods of sensor affixation, the dataobtained is often irreproducible as it is not readily possible to locatethe sensor in the same place on the body each time a test is taken. Mostsensor affixation requires the services of an attendant, especially ifthe sensor must be applied to the patient's back. However, even if it ispossible to reach the desired sensor location, the patient would have tobe specially trained to apply the sensor properly. Further, in caseswhere the electrode is strapped to a patient, the electrode will oftennot stay in the same position if the patient moves.

To estimate blood flow through the heart there are basically twoalternatives. In one alternative, a sensor intrusively enters the bodythrough a vein and through the heart, thereby being a time-consuming,costly and dangerous testing procedure. The alternative method ofballistocardiography involves placing the subject on a special bed andinvolves using a motion transducer to measure body movement caused bythe heart beat. Accurate use of a motion transducer requires that thebody remain still and free from the effects of external movements suchas microseisms in the ground, structural building vibrations, and dorsaltissue vibrations. However a motion transducer connected to a bed oftenyields data confused by spurious oscillating connections between thepatient and the sensor. The prior art suggests that footboards, andlateral clamps or straps, greatly improve the coupling between the bodyand bed, and that the dorsal spring constant can be increased by havinga rough surface on the bed so that when the subject lies on the bed withthe subject's feet against a footboard and knees flexed, full extensionof the legs keeps a high tension in the dorsal tissue all during datataking; however, even the better methods of ballistocardiography havenot produced the reproducibility and accuracy desired. Moreover, thepositioning of the patient with respect to the sensor, electrodes andballistocardiograph bed, or the positioning of the sensors, electrodes,etc., with respect to the patient has required the services of anattendant skilled in the techniques required.

Further, the excitations of body resonances by the familiar physician's"thumping" the chest has up to this time required the active attendanceand participation of a highly trained professional.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prospective top view of a system of the present invention.

FIG. 2 is a side view of a system of the present invention with thesubject's body lying in the body mold depression of the presentinvention.

FIG. 3 is the same view as FIG. 2 with the subject's body raised out ofthe body mold depression of the present invention.

FIG. 4 is an enlarged view of a portion of FIG. 3 showing abody/hammock/body mold sandwich.

FIGS. 5a,b shows the body mold bag of the present invention.

FIG. 6 shows a cross-sectional diagram of the body mold of the presentinvention supported by vertical legs.

SUMMARY OF THE INVENTION

In its broadest sense, the present invention comprises a physiologicalinformation gathering system. The system can be particularly adapted toprovide a method of in-home, self monitorization for elderly, sickly andhealth-concerned persons without the assistance or required presence ofan attendant.

Basic to the system of the present invention is an individually maderigid body mold having a negative impression of the lower half of thebody when the body is in a supine position (a depression intimatelymatching the dorsal half of the body). The body is confined by the bodymold and is held inside it by gravity. In addition to insulating thebody from the effects of external movements, the body mold alsoaccurately and reproducibly positions the body and keeps the bodystationary. By embedding or connecting sensors to the body mold atspecific locations, the sensors will also be accurately and reproduciblypositioned next to a specific body location each time the subject liesin the body mold. As a result, the data gathered by the sensors willprovide accurate and reproducible measurements of physiologicalconditions. Means also are provided for conveniently moving a subject'sbody into and out of the body mold depression. The system overallprovides significant advances in some analytical fields such asballistocardiography, and in many fields, provides a superior method ofreproducibly and accurately gathering physiological data.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description is the best presently contemplated mode ofcarrying out the invention. This description is made for the purpose ofillustrating the general principles of the invention and is not to betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

In general, the present invention comprises a system, apparatus andmethod for gathering physiological data to provide useful physiologicalinformation to the health conscious. In one embodiment of the invention,and with reference to FIGS. 1-4, the system of the present inventionincludes body mold 10 resting on table 20 having flat, planer uppersurface 20a and preferably with four vertical table supports 20b,c (twoare not shown) extending from each corner of the table. The dorsal halfof a body 30 is shown lying in a negative impression 10a of the bodymold 10. Sandwiched between the body 30 and the depression surface isresilient hammock 40. Extending from the top of the table 20, adjacentthe head 30a and feet 30b of the body 30, are motorized hammock rollermechanisms 50a,b. The hammock 40 and the roller mechanisms 50a,bfunction to lift the body 30 out of, and place the body into, body molddepression 10a by making the hammock 40 rigid and flaccid, respectively.Extending from the body mold 10 are connections 60b, 70b, 80 b, and 90bcoupling sensors 60a (the metal bell endpiece of a stethoscope), 70a(electrocardiogram electrode), 80a (thermistor) and 90a (accelerometer)(which are embedded in the body mold 10 adjacent specific locations onthe body) with instruments contained in console 100.

The body mold 10 can be made of any firm, structurally rigid material,such as a polyurethane isocyanate foaming plastic system. If used forballistocardiography, the body mold 10 is preferably made of a lowdensity, high modulus, foaming plastic such as that sold under thetrademark "Structural Rigid Foam" by Polymer Development Laboratories,Inc. The foaming plastic is preferred due to its lightness, its lowthermal conductivity and stiffness.

The body mold 10 can be individually prepared in a variety of ways;however, one way is preferred. With reference to FIGS. 5a,b, a thinplastic or rubber bag 110 having an opening 110a is placed within a moldform 120 (which is removed after mold is made) on a flat surface such asthat of the upper surface 20a of the table 20. Bag opening 110a isadapted to receive nozzle (not shown) of mixing injection pump machine(not shown). Body 30 lies in a supine position on uninflated bag 110.The bag 110 is then injected with a foaming plastic mixture therebysimultaneously raising the patient off of the flat table and creating adepression 10a. By filling the bag about one-half the way up the bodywidth, and allowing the foaming plastic or rubber to solidify, removalof the bag followed by trimming of the rough body mold will reveal thefinished body mold 10. Generally, the low density foam is quick-setting.Some foaming plastics form an integral skin which results in the bodymold having a tough, outer skin. Alternatively, the addition of an epoxycoat to the body mold strengthens the body mold surface.

Another way of preparing the body mold 10 involves cutting the dorsalimpression from a solid plastic foam block. Optical sensor systems areavailable to generate a graphical representation of the subject's bodywhich can be used to properly cut out the dorsal impression. However,since the graphical representation does not include the effects ofgravity on the dorsal tissue, it is not a preferred method.

After the body mold is prepared, or in some cases as discussed belowduring mold preparation, sensors are connected to the mold such thattheir placement, coupled with the force of gravity exerted by the bodywhen the body is in the mold depression, connects the sensors adjacentto specific body locations. Such a sensor is thereby placed inoperational contact with the body portion. In appropriate cases, thesensors can be made flush with or slightly protruding from the mold bymethods well known.

A variety of sensors may be connected to or otherwise embedded in thebody mold 10. For example, stethoscope 60 having metal bell end piece60a, can be, alone or together with microphone 60d or a thumper,embedded in mold 10.

The stethoscope metal bell end piece can be counter-sunk into the mold10, with it preferably slightly protruding. The stethoscope can bemounted by drilling a hole having a diameter slightly larger than thesensor using a rotary tool having course burr, and counter-sinking themetal bell. Alternatively, the stethoscope bell can be taped to the bodywhen the body mold is being prepared thereby simultaneously generatingan impression for the stethoscope metal bell. Stethoscope 60 can belistened to via earphones (not shown) or the data received by it can befed to an electronic microphone and amplifier coupled to the console100. And, by listening to the stethoscope bell sounds in response toeach activation of the thumper, body resonances can be determined.

As discussed below, other sensors can be embedded the same way or tapedto the body during molding such as an electrocardiogram electrode 70 fordetermining a subjects heart rate by analyzing the amplified electrodevoltage of the electrocardiogram electrodes, a thermistor or temperaturetransducer 80 for estimating temperature by recording the voltage outputof the temperature transducer, and an accelerometer 90 as discussed indetail below. Other electrodes and sensors include impedencepneumography electrodes which are used to measure respiration frequencyand crude depth of respiration, skin color sensors or transducers whichcan be placed adjacent specific body locations to determine oxygensaturation of the hemoglobin, pneumocardiogram electrodes, verticalforce transducers, transdermal blood oxygen sensors and transdermalblood carbon dioxide sensors for estimating blood oxygen and carbondioxide tension, respectively, heart and lung sound sensors, and lungresonance sensors.

With reference to FIG. 6 the body mold can also be used to estimate boththe weight and the horizontal component of the center of gravity of thepatient by placing an appropriate sensor and amplifier on each of thevertical supports on the bed, and computer-solving the appropriateequations. Specifically, body mold 10 is firmly affixed to table or bed20 which is connected by springs 25a,b to rigid frame 35. The bed 20 isconnected by low friction axles 35a,b,c,d to rigid vertical supports35e,f which are in turn connected to pedestals 35g,h, each having aweight or vertical force transducer (not shown) including apreamplifier. It should be appreciated that only two vertical supportsare shown, but that there are four identical ones in total, oneconnected to each of the four corner areas of the bed. The signals fromthe transducer are fed via wires 35i,j to a console for analysis by anappropriate computer. It should also be appreciated that the bedvertical supports are wide in the perpendicular (horizontal) directionso as to facilitate restraining the bed so that it cannot move sideways.

In the art of ballistocardiography, the slight movement of the body ismeasured as the body reacts to the blood inertia forces caused by theheartbeat. A motion transducer or more specifically an accelerometer maybe used to generate a ballistocardiogram which is basically a time-basedchart of body acceleration, velocity or position data. Recordation ofsuch data into chart form enables one to estimate the heart action andheart output of a patient relative to a previously recorded "baseline".

In the preferred method where ballistocardiography is included, anaccelerometer is embedded in the body mold so that its longitudinal axiss along the longitudinal axis of the body. This is done by making a holein the mold, inserting the accelerometer, and gluing the accelerometerto the mold. The mold will move in response to the heartbeat, and thelongitudinal vibrations will be recorded by the accelerometer. Byembedding the accelerometer 90a in the body mold 10, aballistocardiogram sensor is accurately placed with respect to specificbody portions; the body mold keeping the body still and free of theeffects of its own oscillations vs. the bed and external movements. As aresult, reproducible data can be obtained and accurate comparison withprevious data performed.

To obtain a ballistocardiogram, the body mold may rest upon extremelyslippery horizontal linear bearings, or rest upon vertical legs (seeFIG. 6), in each case constraining the body mold so that it can onlymove in the longitudinal direction "n".

The system of the present invention is particularly useful to theelderly and invalid. The system can include a transfer mechanism toenable conveniently transferring the body 30 into and out of the bodymold 10. The transfer mechanism includes head roller mechanisms 50a,foot roller mechanisms 50b, supports 50c and d, and rollable hammock 40having one end connected to roller mechanism 50a and the other endconnected to roller mechanism 50b. A motor drive 55a,b is provided forthe head roller and the foot roller, respectively. The hammock can bemade of a cloth sheet or membrane, for example, a nylon knitted fabricwhich is silky, flexible, thin and relatively non-distensiblelongitudinally. The hammock contains reinforced holes positioned toallow the electrodes and sensors to contact the skin.

While the body mold is being used, the motors are not activated therebymaintaining the hammock flaccid. The hammock therefore does notsignificantly effect the contours of the body mold depression. When themotors are forwardly activated, the hammock is tightened. At that point,the subject merely lies down on the hammock. The motors are thenoperated slowly in reverse to render the hammock flaccid therebysimultaneously placing the body into the depression. After testing iscomplete, the motors are again forwardly activated to render the hammocktaut. The subject can then easily get off of the hammock. Compare thehammock depicted in FIGS. 2 and 3.

There are a wide variety of variations of the above description whichthose of skill in the art will recognize as being within the scope ofthe present invention. For example, the present invention, in oneaspect, contemplates a revolution in medical technology. Specifically,the present invention envisions accurate in-home self-monitorization.That is, the body mold "bed" is relatively inexpensive, and can be keptin the home of any person, for example, the elderly and sickly, and usedto obtain, as well as transmit, vital sign data to a physician, withoutthe assistance of another person.

I claim:
 1. A method for determining the horizontal component of asubject's center of gravity and body weight, the method comprising thesteps of:placing the subject's body horizontally in a substantiallyrigid body mold having an impression exactly matching the dorsal half ofthe body, the body mold being supported by supporting members; attachinga vertical force transducer to each of the supporting members; andanalyzing the amplified outputs of the force transducers to compute thesubject's body weight and horizontal center of gravity.
 2. The method ofclaim 1 wherein the subject's body is placed in the body mold by firstlaying the subject on a thin, flexible sheet, and then lowering thesheet bearing the subject into the impression.
 3. A method fordetermining the change in the horizontal component of a subject's centerof gravity and body weight, the method including the steps of:placing abody in a substantially rigid body mold having an impression exactlymatching the dorsal half of the body, the body mold being supported bysupporting members fixed with respect to the body mold; attaching avertical force transducer to each of the supporting members; analyzingthe amplified outputs of the force transducers to compute the subject'sbody weight and horizontal center of gravity; and comparing the computedvalues with previously known values to determine the change in thebody's horizontal center of gravity and weight.